Process for enhancing control over a braked vehicle

Details Process for enhancing control over a braked vehicle Process for enhancing control over a braked vehicle

1990-11-26

1993-05-18

Oberleitner, Robert J.

Fluid-pressure and analogous brake systems

Speed-controlled

Having a valve system responsive to a wheel lock signal

303 241, 3031135, 36442602, B60T 860

Patent

active

052114538

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



Prior art

The invention relates to a method of improving the control of a vehicle during braking by changing the brake pressure at the wheels.
Methods which serve to improve the control over a vehicle are, for example, anti-lock brake control systems and drive-slip control systems. In conjunction with ABS, it is also known to employ yaw torque decrease and select-low-control both of which further improve control over a vehicle.


SUMMARY OF THE INVENTION

The transverse-stability reserve TSR is a measure for the instantaneous slope in the operating point of the inclined-position curve. In the method of the invention it can be described as follows: ##EQU1## wherein
by,o is the initial value of the transverse acceleration
by,p is the transverse acceleration of the wheel during the brake slippage pulse
by,n is the transverse acceleration of the wheel after the brake slippage pulse.
The inclined-position curve is the known relation between the angle of the inclined position of the wheel and the lateral adhesion coefficient .mu..sub.s.
The method in accordance with the invention can be used in vehicles with anti-lock brake control and/or drive slip control. These control methods are known to involve relatively long phases where the brake pressure is maintained at a constant level.
As compared to the prior art, where no statements are made on how stable and steerable a vehicle is during braking, the method of invention seeks to make such a statement in order to vary the slippage for the purpose of improving the control over the vehicle. The core of the invention is the determination of the transverse stability reserve of a vehicle axle. As already mentioned, this transverse stability reserve is a measure for the instantaneous slope, i.e. the local slope in the operating point of the inclined-position curve. When the local slope of the inclined-position curve is steep, then the transverse-stability reserve is high and an increase of the angle of the inclined position causes the adhesion coefficient for the lateral forces to greatly increase. When the local slope of the inclined-position curve is small, then transverse-stability reserve is small and an increased inclined-position angle causes the adhesion coefficient for the lateral forces to increase only to a small extent. In case the local slope of the inclined-position curve is negative, the transverse-stability reserve is also negative and an increased inclined-position angle causes the adhesion coefficient for the lateral forces to decrease.
The transverse-stability reserve is hence a measure for the lateral force reserves at the axles. A change of the brake slippages causes a change of the transverse-stability reserves and hence improves the steerability and the stability of the vehicle and/or prevents a skidding or pushing of the vehicle.
The aforesaid is based on the following considerations. Brake force and/or brake slippage of tires are known to greatly affect the transverse dynamics of a vehicle, i.e. steerability and stability thereof Generally, it can be said that longitudinal slippage at the rear wheels reduces stability. Modifying the brake slippage at the front and rear wheels can hence improve or impair steerability and stability of a vehicle. A decrease of the longitudinal slippage at the front wheels and an increase of the longitudinal slippage of the rear wheels, for example, increases the yawing tendency (steerability) of a vehicle. Vice-versa, it is possible to decrease the yawing tendency of the vehicle by increasing the longitudinal slippage at the front wheels and decreasing the longitudinal slippage at the rear wheels which means the vehicle will be stabilized. Similarly, the curve radius at the front and rear wheels can be reduced by decreasing the longitudinal slippage.
The above made statements also apply to drive slippage even though longitudinal slippage is subsequently referred to as brake slippage.
The question that arises is whether the brake slippage must be increased or decreased at the respectiv

REFERENCES:
patent: 4647115 (1987-03-01), Leiber et al.
patent: 4758053 (1988-07-01), Yasuno
patent: 4794539 (1988-12-01), Wallentowitz et al.
patent: 4898431 (1990-02-01), Karnopp et al.
patent: 4967865 (1990-11-01), Schindler
patent: 4998593 (1991-03-01), Karnopp et al.
Bosch Technische Berichte, Heinz Leiber et al. "Antiskid System (ABS) for Passenger Cars", English Special Edition (Feb. 1982).

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